Known work stations use a specific CPU, e.g. an Intel 80386 microprocessor provided on a system board together with other chip units such as memories, various peripheral interfaces and a system bus controller. The CPU and the above mentioned units communicate with each other, partially through buffers, over a local bus comprising control, address and data lines, all units being under tight control of the CPU through the local bus. In general, the system design is tailored for the specific CPU. This means that a large variety of different chip units are required for work stations using different CPUs. The local bus also is tailored for the specific configuration. In order to maintain compatibility with other systems, detailed specifications rigidly determine the features and functions of the various units and their I/O registers. Thus, it is difficult to modify the system for expansion and improved performance.
Specifically, any communication such as writing to or reading from memories is completely controlled by the CPU or any other unit adapted to be bus master for the local bus. This means that functions relating to a specific unit only, such as refreshing of memories or clearing of overflow situations in cache memories are performed under control of the CPU resulting in a time consuming procedure with many interruptions of normal processing.